Servo loading stand



June 16, 1953 s. P. ALTMAN SERVO LOADING STAND 3 Sheets-Sheet l IN VEN TOR.

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Junelalesa S.'P.A| TMAN,

SERVO LOADING STAND 3 Sheets-Sheet 2 FiledOCt. 3. 1950 mm MM w y p W 4 June 16, 1953 s. P. ALTMAN I 2,641,925

SERVO LOADING STAND Filed Oct. 3, 1950 3 Sheets-Sheet 5 INVENTOR. .5w/wa A( 7M/mf armen/a Patente-d June 16, 1953 UNITED v STM-13s PATENT OFFICE 2,641,925 y y sEvo LOADING STAND samuel P. Altman, Daytom'ohiq Application October 3, 1950, Serial No. 188,256 l claims. (c1. vis- 116) (Granted under Title 35, U. S. Code `(1952),

sec. '266) v The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to laboratory apparatus and has special reference to a stand for analyzing the dynamic performance of the servomotor of an automatic pilot under various load conditions which are imposed on the output shafts of the servomotors. y

The apparatus is designed to subject the autopilot servomotor to inertia, spring, and damping loads which are the equivalent of those encountered in actual aircraft flight. Thus, once having determined the specific load conditions which will be encountered in a particular aircraft installation, the apparatus may be set to duplicate these conditions, whereby the dynamic performu ance of the servomotor may be observed by sub- 'jecting the servo, as it operates against its various loads, to a sinusoidal, step function, or any other form of input signal, and recordings of in- .put and output made on oscillographs or other types of recorders. The apparatus is so designed that its loads may be varied over a considerable range so as to simulate the characteristics of many different types of aircraft.

In the drawings which illustrate one embodiment of the invention,

Fig. l is a side view of the assembled machine.

Fig. 2 is a top plan view of the mechanism shown in Fig. 1. Y

Fig. 3 is an end view of the device shown in Fig. 1 looking from the right toward the left.

Fig. 4 is an enlarged top plan view of the main loadingshaft whichappears to a smaller scale -inFig. 2.

.Fig. 5 is an enlarged vertical section through the mainV loading shaft taken at 5-5 of Fig. 2. Fig. 6 is an enlarged vertical section through the spring adjusting mechanism taken at 6--6 of Fig. l.

AIn all of the foregoing views like reference characters refer to like parts.

,- In the drawings, a main frame l0 comprises two parallel base members I2 with diagonal end *legsV i4 and intermediate legsA I6 extending upl wardly from the base members to support the bed rails I8. Cross braces 20 prevent spread of the base members I2. The several instrumenytalities for making the tests on the servomotors are mounted on the bed rails I8 andbase members l2.

Supported on the left end of the bed rails I8 isjlthelservo mounting carriage 22 which` consists of a base plate 24 upturned at the ends to provide support for a rod 26 and a screw 28. A carriage 'platen 30 is slidable on the rod 26 and is internally threaded for the screw 28. A hand wheel 32 is afiixed to the outer end of the screw 28 whereby the screw may be turned to move the platen 30 longitudinally on the machine. A plurality of T'slots 34 (see Fig. l) may be provided for the heads of bolts, whereby the servomotor 3G may be rigidly mounted on the platen 30. A servo output drum 38 is fast on the outer end of the servomotor shaft 40.

The body of the loading apparatus 42 is secured to the bed rails I8 at a point intermediate from the ends, and comprises a base plate 44 with side members 46 extending upwardly therefrom, and antifriction bearing cases 48 carried on the forward edges of the side plates.

Bearing cases 48 contain antifriction bearings 50 (see Fig. l) which rotatably support the main loading shaft 52. Shaft 52 is shown to an enlarged scale in Figs. 4 and 5. A grooved pulley 53 is fastened to the outer end of the main loading shaft 52, and a cable 55 spans the servo output drum 38 and the pulley 53. Pulleys of different diameters may be substituted for the pulley 53. The tension in the cable 55 may be adjusted by means of the hand wheel 32.

In the space between the antifriction bearings 50, the shaft 52 has an elongated hub 54 (see Fig. 4) which has integral therewith ytwo arms 56 and 58 extending more or less horizontally toward the right, the arms at the extreme right end being provided with short hubs 60 (see Fig. 4) through which a short shaft 62 extends.

Freely turnable on the short shaft 62 are longer hubs 64 and 66 (see Fig. 4) which are provided respectively lwith arms 68 and 'l0 which extend from their pivotal point toward the left. The left portion of the arms 68 and 'lll are of arcuate contour on the outer edge 12 (see Fig. 5), the center of the arcs being at the center of the main loading shaft 52 when the internal flats of the Z shaped members 16 are parallel. The arms 68 and 'l0 are offset at 14, Fig. 4, so that the left half of the arms are one above the other in the same plane, armv 68 being below and arm 1li being above (see Figs. 4 and 5). These arcuate portions 12 and their grooves 13 constitute, in effect, a grooved pulley the diameter of which may be varied while the apparatus is in operation.

Z shaped members 16 are attached, one to the upper arm 10 and another to the lower arm 58, by screws 18 (see Figs. 4 and 5), whereby pockets areY formed for the right and left hand nuts 80 and 82. Pivoting screws 84 extending through the arms 68 and 'I0 and through the Z shaped members into nuts 80 and 82 hold the nuts in place. A screw 85, khaving the upper end threaded left hand and the lower end threaded right hand, if turned clockwise, viewed from above, will decrease the average radius from the center of the main loading shaft to the surfaces 12 (see Fig. 5), while anticlockwise rotation of the screw will increase the average radius.

A bracket 86 (see Fig. 5) is fastened to the mainloading shaft 52 by screws 88 and has a tongue 90 which extends into a groove in an enlarged part 32 of the screw 85, whereby rotation of the screw 85 always moves the arms 68 and l equal amounts in or out, and as long as the screw S remains nonrotative it prevents movement of the arms 68 or 10 toward or way from the axis of the loading shaft 52. An arcuate bracket 54 is fastened to the arm 63 by screws 96 whereby the average radius of the arcuate surfaces 'l2 from the center of the main loading shaft 52 may be read on the graduations S6 on the bracket. A pointer |05 for the graduation 68 is fastened to the member 'i5 by screws |02.

rfhe outer convex surfaces l2 of the arms 68 and 'i0 (see Figs. 4 and 5) are grooved as at 13 for the cables 555i and |55, the rear ends of the cables being provided with cable-ends which are tted to sockets ii in the extreme left end of the arms 53 and i5. Pull on one or the other of the cables |53 or |54 rotates the loading shaft 52 clockwise or anticlockwise. A pointer |55 on the right hand end of the arm 58, rigidly fixed against rotation about the axis of the short shaft E2 by a pin 45'? (see Fig. 5), corresponds with the graduations of chart lili) (see Figs. l and. 2) to measure the degree of rotation.

By means of the above arrangement there is provided, for the purposes of this apparatus, the equivalent of an infinitely variable diameter pulley which `can be varied in diameter while the test is progressing. The infinitely variable diameter pulley adjustable to simulate a spring load.

A long bar l0 is mounted fast on the forward end of the main loading shaft 52 and is provided at its ends with weights ||2 which are made in different sizes so that they can be changed to simulate different inertia loads.

A large aluminum segment H4 (see Figs. 1 and 4) is fastened to the side of the arm 58 by bolts i i5 whereby the segment is turnable as one with the shaft 52. The lower end of the segment ||l swings freely in the air gap between the poles of an electromagnet H6 (see Fig. 1), thereby simulating a particular aircraft control surface damping load. force proportional to the rate of motion through the air gap is obtained, due to eddy currents the segment. The damping load can ce varied by changing the amount of current energizing the electromagnetic coils.

The electromagnet H6 comprises a laminated core ii held between angle brackets which are fastened to a transverse plate |22 which rests on the base members i2, the angle brackets |20 and the plate if? being fastened to the base member i2 by bolts |24. Two -electromagnet windings E26 are wound around and secured to poles of the core H5. A rheostat H9 controls the D. C. current from the source |2|.

On the extreme right end of the bed rails i8 there is mounted a tail stock assembly which carries a precision adjusting means for each of the springs |30 and |32. These adjusting means each comprise a worm shaft |34 and a worm wheel shaft |36 rotatable respectively in antifriction bearings |38 and |40. Shaft |34 is provided with a worm thread |42 while shaft |36 is multiple splined as at |44, Fig. 3 or 6, for a small internally splined pulley |46. Pulley |46 is slidable axially on the shaft |36 for aligning itself with the cables |04 and |06. Short cables |43 and |50 have one end connected to springs |30 and |32 and the other ends to the surface of small pulleys |46, whereby the preload tension in springs |30 or |32 may be adjusted by rotation of the hand wheels |52 or |54.

A signal device |56, Fig. 1, is provided so that a D. C. or A. C. signal, proportional to and in phase with the displacement of the servo shaft 40, may be obtained for recording or indicator purposes.

An arm |58 having a pivotal point |60 at its outer end is xed to the rotor shaft |52 of a synchro |64 The shaft of the synchro |64 is geared to contact wiper assembly |53 of the potentiometer i55. A lug- 555 on the loading shaft 52 has its pivotal point |58 at the same radius from the axis of the loading shaft 52 as the pivotal point |55 of thearni |53 is distant from the axis |62 of the synchro. f

A rod l 'i5 has a clevis |72 at the upper end and another clevis |74 at the lower end for connecting the pivots |55 and |58 together. The pivotal points |55. and |68 at the ends of the rod |10 are as far apart as the axis of the synchro |64 is distant from the axis of the loading shaft 52.

Some of the advantages of the invention herein disclosed are as follows:

l. All loads are applied to the main loading shaft and adjusted before the auto pilot servo which is to be tested is itself placed under load.

2. The damping load is viscous damping; that is, the for-ce is proportionate to the rate of angular displacement only for a given magnet coil current.

3. The effective spring constant can be changed without changing the spring itself by the use of th-e variable adjustment loading shaft, which may be done by providing an electric motor for turning the adjusting screw of the loading shaft in response to an electrical signal.

4. The damping load can be adjusted or changed during the test by proper electrical control of the current in the electromagnet.

The possibility of adjusting the several loads during the test is very important for aircraft with non-linear control surface loads.

Having described my invention, I claim:

1. Apparatus for testing servomotors which comprise in combination a frame, a servomotor mounting means adjustably mounted on the frame, a loading shaft mounted on said frame with is axis arranged so as to be parallel with the shaft of a servomotor on said mounting means, adjusting means associated with the servomotor mounting means for adjusting the distance between the servomotor shaft and the loading shaft, pulley and cable means connecting the shafts, means mounted on the loading shaft for applying a predetermined inertia load thereto, means operatively associated with the loading shaft for applying a predetermined viscous load thereto, further means connected to the. loading shaft for applying a predetermined spring load thereto, means associated with the viscous load means for varying the viscous load while test is in progress and means cooperatively engaging the spring load means for varying the spring load means while the test is in progress.

2. Apparatus for testing servomotors which comprises in combination a frame, a servomotor mounting means on said frame, a loading shaft mounted on said frame with axis parallel with the shaft of the servomotor, means for adjusting the distance between said shafts, pulley and cable means connecting said shafts, means for applying a predetermined inertia load to said loading shaft, means for applying a predetermined viscous load to said loading shaft, means for applylng a predetermined spring load to said loading shaft, and means for varying the viscous load and means for Varying the spring load, both while said test is in progress, the means for applying a predetermined inertia load` to the loading shaft consisting of a long bar fast at its midpoint to the end of said loading shaft and a selected pair of weights affixed one Weight at each end of the bar.

3. Apparatus for testing servomotors which comprises in combination a frame, a servomotor mounting means on said frame, a loading shaft mounted on said frame with axis parallel with the shaft of the servomotor, means for adjusting the distance between said shafts, pulley and cable means connecting said shafts, means for applying a predetermined inertia load to said loading shaft, means for applying a predetermined viscous load to said loading shaft, means for applying a predetermined spring loadto said loading shaft, and means for varying the viscous load and means for Varying the spring load, both While said test is in progress, the means for applying a predetermined viscous load to the loading shaft comprising an electromagnet fast on said frame with spaced apart poles, and a segment concentric with the loading shaft axis and secured thereto and positioned thereon to extend into and rock between said poles thereby L f generating eddy currents which vary with the speed at which the segment rocks, and vary with the current in the electromagnet coils.

4. Apparatus for testing servomotors which comprises in combination a frame, a servomotor mounting means on said frame, a loading shaft mounted on said frame with axis parallel with the shaft of the servomotor, means for adjusting the distance between said shafts, pulley and cable means connecting said shafts, means for applying a predetermined inertia load to said loading shaft, means for applying a predetermined viscous load to said loading shaft, means for applying a predetermined spring load to said loading shaft, means for varying the viscous load and means for varying the spring load, both while said test is in progress, the means for applying' a predetermined spring load to the loading shaft consisting of a pair of substantially parallel cables one spaced from the other in substantially the same plane, two small shafts spaced apart from and parallel to the loading shaft, a small pulley 'axially slidable on but drivably connected to each said small shaft, a split pulley on the loading shaft, the one cable passing clockwise partway around the one half of said split pulley and the other cable passing anticlockwise partway around the other half thereof, cable ends on said cables adapted to t into sockets in the halves of said split pulley, one end of each cable being thereby operatively secured tothe loading shaft, the opposite end being attached to the circumference of said small pulley, separate adjusting means for rotating said small pulleys to tauten said cables, an extension coil spring interposed within the length of each cable, and adjusting means to spread apart the one half of said split pulley from the other half.

5. The apparatus of claim 4 wherein the diameter of the split pulley on the loading shaft is adjustable while the apparatus is in operation.

SAMUEL P. ALTMAN.

References Cited in the le of this patent UNITED STATES PATENTS 

